P. Salonen and R. Koskinen (Finland)
Adaptive antenna, LMS Algorithm, Digital beamforming, WLAN, RFID.
Spatial filtering using adaptive or smart antennas has emerged as a promising technique to improve the performance of cellular mobile systems. The cancellation of interfering signals and the protection of a target signal are based on an adaptive algorithm. In this paper a comparison analysis of four LMS variants, namely basic LMS, normalized LMS (NLMS), clipped LMS, and zero forcing LMS, for small antenna arrays is carried out. We have used 5, 9, and 25-element antenna arrays in the study for beamforming accuracy in the presence of interfering signals near the target. In addition, the learning curves are studied for 30dB and 60dB signal-to-noise ratio (SNR) for all test arrays. The results showed that even the standard LMS algorithm is very capable in WLAN and RFID applications. In addition, the standard LMS and NLMS are computationally fast enough. Therefore, the standard LMS and NLMS seem to be more suitable for various and inexpensive digital signal processors and microprocessors. As a result this will keep the costs to a minimum.
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